Mapper2

好的，以下是一个使用动态类和@SelectProvider的完整代码示例：

1. 定义Mapper接口：

@Mapper
@Repository
public interface MyMapper {
    @SelectProvider(type = SqlProvider.class, method = "selectSql")
    List<Result> selectData(Map<String, Object> params);
}

1. 定义SqlProvider类：

public class SqlProvider {
    public String selectSql(Map<String, Object> params) {
        String tableName = (String) params.get("tableName");
        String columnNames = (String) params.get("columnNames");

        String sql = String.format("SELECT %s FROM %s", columnNames, tableName);
        return sql;
    }
}

1. 定义动态类ResultSetMapper：

public class ResultSetMapper<T> implements ResultSetHandler<List<T>> {
    private Class<T> clazz;

    public ResultSetMapper(Class<T> clazz) {
        this.clazz = clazz;
    }

    @Override
    public List<T> handle(ResultSet rs) throws SQLException {
        List<T> list = new ArrayList<>();
        ResultSetMetaData metaData = rs.getMetaData();
        int columnCount = metaData.getColumnCount();

        while (rs.next()) {
            T obj = null;
            try {
                obj = clazz.newInstance();
            } catch (InstantiationException | IllegalAccessException e) {
                e.printStackTrace();
            }

            for (int i = 1; i <= columnCount; i++) {
                String columnName = metaData.getColumnLabel(i);
                Object columnValue = rs.getObject(i);
                setProperty(obj, columnName, columnValue);
            }

            list.add(obj);
        }

        return list;
    }

    private void setProperty(T obj, String propertyName, Object value) {
        try {
            Field field = obj.getClass().getDeclaredField(propertyName);
            field.setAccessible(true);
            field.set(obj, value);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

1. 调用Mapper接口方法：

@Autowired
private MyMapper myMapper;

public List<Result> selectData() {
    Map<String, Object> params = new HashMap<>();
    params.put("tableName", "my_table");
    params.put("columnNames", "column1, column2, column3");

    ResultSetMapper<Result> mapper = new ResultSetMapper<>(Result.class);
    return myMapper.selectData(params).stream().flatMap(Collection::stream).map(mapper::handle).collect(Collectors.toList());
}

在这个例子中，使用了@SelectProvider注解来指定SQL查询语句。SqlProvider类的selectSql方法返回SQL查询语句字符串。在Mapper接口方法中，调用了动态类ResultSetMapper来将查询结果映射成List。